The connector on the back of most ATX power supplies sold in the UK is an EN 60320 -1 IEC C14 Class I Cold Condition connector, rated at 10A 250V. The mating connector on the flying lead/cord/cable/et al, is an IEC C13 with the same rating.
https://standards.globalspec.com/std/14478346/en-iec-60320-1
Interestingly, for USA and Canada, the UL/CSA rating for C13 and C14 connectors increases to 15A 250V. Where they get this extra 50% current rating from I don't know. Perhaps one set of standards is more relaxed, due to operating at 120V most of the time.
Thus in the UK, the cross sectional area of the conductors needs to be rated at 10A maximum, but I guess in the States and Canada, it might have to be 15A.
In case you're wondering, a Hot Condition C15/C16 plug/socket combination is the type of connector used in appliances that get hot, e.g. some electric kettles. Note the cut out to prevent idiots plugging a Cold Connector into a hot appliance and "melting" the connector. People who call computer leads "kettle" leads don't know what they're talking about (end of rant).
And finally, you can argue semantics as to what to call the bendy stuff between the two connectors, depending on what country you live in.